Opposition leaders say the thousands killed at the hands of Assad's security forces, many while protesting peacefully, mean they will accept nothing less than Assad's ouster and the end to his family's 40-year dynasty in Syria.

Assad is not willing to give an inch, either. On Sunday, he said a political solution is impossible as long as Syria is being threatened by "terrorist groups" — the regime's term for its opponents. His comments all but ensured the military crackdown will continue indefinitely, as Assad tries to crush an uprising that has transformed into an armed insurgency.

Neither side has scored a decisive blow in the conflict, which already has killed more than 7,500 people over a year of ferocious turmoil. Both parties are holding out for absolute victory, convinced their goals are within reach.

However, The New York Times reports that senior military officials have ratcheted up their warnings that an intervention would be a “daunting and protracted operation, requiring at least weeks of exclusively US airstrikes, with the potential for killing vast numbers of civilians and plunging the country closer to civil war.”

Officials say that Syria is a far more complicated situation than Libya, where the US staged a military intervention last year.

… Defense officials say they are concerned about four tough challenges: the risks in attacking Syria’s plentiful and sophisticated Russian-made air defenses, which are located close to major population centers; arming a deeply splintered Syrian opposition; the potential for starting a proxy war with Iran or Russia, two crucial allies of Syria; and the lack, at least so far, of an international coalition willing to take action against the government of President Bashar al-Assad.

At a UN Security Council meeting yesterday, the US and Russia were once again at loggerheads over next steps to address the crisis. The Russian representative at the meeting “joked with reporters that he wished Russia has as much influence in Syria to resolve the crisis as some people believe,” according to The Wall Street Journal.

At the U.N., Russian Foreign Minister Sergei Lavrov condemned what he called support for terrorists by foreign governments, which he didn't name, in an attempt to overthrow the legal authorities in Damascus. He also railed against the arming of the Syrian population. "Interference from outside, using raw military force, increases the illicit spread of arms," Mr. Lavrov said, "thus jeopardizing stability in the region."

Secretary of State Hillary Clinton suggested Russia was guilty of standing silent while the Assad regime killed its own people. She portrayed Syria's crisis as a legitimate revolt of the Syrian people against a dictatorial regime. "We reject any equivalence between premeditated murders by a government's military machine, and the actions of civilians under siege driven to self-defense," she said.

Mr. Lavrov said that while the Syrian government bears some of the responsibility for the violence, it has been fighting more than unarmed men; it has been fighting combat groups that include Al Qaeda, WSJ reports.

Russian Deputy Defense Minister Anatoly Antonov said today that Russia will fulfill the terms of its existing arms contracts with Syria, telling reporters that Russia has “good, strong military technical cooperation with Syria, and we see no reason to reconsider it,” the Associated Press reports.